Geometry Problem
In the figure below, AOB is a circular sector of 90° degrees. C is a point on arc AB, ACDE and CBFG are squares. Prove that 
(For C = B the formula is  Pythagoras' theorem for the right  triangle  ODH)
http://gogeometry.com/school-college/1/p1022-circular-sector-90-degrees-squares-metric-relations-online-math.htm